1. Field of the Invention
The present invention relates to an electromagnetic switching apparatus, and more particularly, to an electromagnetic switching apparatus capable of having a simplified structure and capable of preventing the occurrence of noise.
2. Background of the Invention
An electromagnetic switching apparatus serves to supply a current to a load or to interrupt current supply to the load, by opening and closing a contact by an electromagnetic force. This electromagnetic switching apparatus is used at equipment for industry, machines, vehicles, etc.
The electromagnetic switching apparatus includes a fixed contact, a movable contact and a driving unit. As the driving unit drives the movable contact by using an electromagnetic force, the movable contact moves to contact or be separated from the fixed contact. As a result, a current is supplied to a load, or current supply to the load is interrupted.
According to the recent trend that various apparatuses have minimized sizes in all the industry fields, the electromagnetic switching apparatus is also required to have a minimized size. In order to implement an electromagnetic switching apparatus having an enhanced reliability, an impact or frictional noise occurring by motions of the driving unit of the electromagnetic switching apparatus may be prevented to the maximum.
FIG. 1 is prior art and illustrates a partial sectional view of one example of an electromagnetic switching apparatus using a shaft. The electromagnetic switching apparatus 100 of FIG. 1 comprises a fixed contact 110, a movable contact 120, a driving unit 130 and a case 140.
The fixed contact 110 includes a first fixed contact 111 connected to a power input, and a second fixed contact 112 connected to a load. For instance, the fixed contact 110 may be fixedly-installed at an upper part of the case 140.
The movable contact 120 is configured to contact or to be separated from the fixed contact 110. When the movable contact 120 contacts the fixed contact 110, the first fixed contact 111 and the second fixed contact 112 are connected to each other by the movable contact 120. Accordingly, power input through the first fixed contact 111 is supplied to a load through the second fixed contact 112.
When the movable contact 120 is separated from the fixed contact 110, the first fixed contact 111 and the second fixed contact 112 are disconnected from each other. Accordingly, power input through the first fixed contact 111 is not supplied to a load through the second fixed contact 112.
The driving unit 130 drives the movable contact 120 by using an electromagnetic force, thereby controlling the movable contact 120 to contact or to be separated from the fixed contact 110. The driving unit 130 includes a fixed core 131, a movable core 132, a shaft 133 and a coil 134.
The fixed core 131 attracts the movable core 132 by an electromagnetic force. For instance, the fixed core 131 may be fixedly-installed at a lower part of the case 140, and may be provided therein with a recess for passing a shaft 133 therethrough.
The movable core 132 is installed below the fixed core 131, and is moved by an electromagnetic force. Once an attractive force occurs between the fixed core 131 and the movable core 132 by an electromagnetic force, the movable core 132 approaches to the fixed core 131. However, once the electromagnetic force does not occur any longer, the movable core 132 is spaced from the fixed core 131 by gravity.
One side of the shaft 133 is coupled to the movable core 132, and another side thereof is coupled to the movable contact 120. Under this configuration, the shaft 133 transmits, to the movable contact 120, a driving force of the movable core 132 due to an attractive force occurring between the fixed core 131 and the movable core 132 by an electromagnetic force, thereby allowing the movable contact 120 to come in contact with the fixed contact 110.
Once the electromagnetic force does not occur any longer, the movable core 132 is spaced from the fixed core 131 by gravity. As a result, the movable contact 120 coupled to the movable core 132 is spaced from the fixed contact 110.
The coil 134 is installed near the fixed core 131 and the movable core 132, and forms a magnetic field at the periphery thereof when a current is applied thereto. By the magnetic field, a magnetic flux is generated at the fixed core 131 and the movable core 132 to generate an electromagnetic force. The fixed core 131 and the movable core 132 form a magnetic path through which a magnetic flux passes. And, an attractive force occurs between the fixed core 131 and the movable core 132 by an electromagnetic force due to a magnetic flux.
The case 140 is formed of a non-magnetic and non-conductive material, and includes upper and lower cases 141 and 142 configured to hermetically cover the fixed contact 110 and the movable contact 120 from the outside, a plunger cap 143 configured to accommodate therein the fixed core 131 and the movable core 132 in a hermetic manner, and a coil cap 144 configured to accommodate therein the coil 134 in a hermetic manner.
Here, the fixed contact 110 may be fixedly-installed at the upper case 141, and the fixed core 131 having a recess for passing the shaft 133 therethrough may be fixedly-installed at the lower case 142.
In a hermetic space formed as the upper case 141 and the lower case 142 are coupled to each other, may be filled gas for extinguishing an arc occurring when the movable contact 120 is separated from the fixed contact 110.
An operation to contact the movable contact 120 to the fixed contact 110 of the electromagnetic switching apparatus will be explained. Once a current is applied to the coil 134, a magnetic field is formed at the periphery of the coil 134, and a magnetic flux is generated at the fixed core 131 and the movable core 132. As a result, an electromagnetic force is generated.
If the coil 134 is wound on the fixed core 131 and the movable core 132 so that facing parts of the fixed core 131 and the movable core 132 can have different polarities, an attractive force is generated. As a result, the movable core 132 is moved toward the fixed core 131. Here, the attractive force should be greater than the gravity.
A driving force is transmitted to the shaft 133 having one side coupled to the movable core 132, and thus the movable contact 120 coupled to another side of the shaft 133 is moved to contact the fixed contact 110.
Once the movable contact 120 comes in contact with the fixed contact 110, the first fixed contact 111 and the second fixed contact 112 are connected to each other by the movable contact 120. Accordingly, power input through the first fixed contact 111 is supplied to a load through the second fixed contact 112.
An operation to separate the movable contact 120 from the fixed contact 110 of the electromagnetic switching apparatus will be explained. Once a current is not applied to the coil 134 in a contact state between the fixed contact 110 and the movable contact 120, a magnetic field formed at the periphery of the coil 134 disappears, and a magnetic flux generated at the fixed core 131 and the movable core 132 also disappears.
As a result, an attractive force between the fixed core 131 and the movable core 132 disappears, and only the gravity is applied to the movable contact 120. Therefore, the movable contact 120 drops by the gravity, and a driving force is transmitted to the shaft 133 having one side coupled to the movable core 132. As a result, the movable contact 120 coupled to another side of the shaft 133 also drops to be separated from the fixed contact 110.
Once the movable contact 120 is separated from the fixed contact 110, the first fixed contact 111 and the second fixed contact 112 are disconnected from each other. Accordingly, power input through the first fixed contact 111 is not supplied to a load through the second fixed contact 112.
However, in the electromagnetic switching apparatus using the shaft of FIG. 1, the movable core and the movable contact are connected to each other by the shaft, and thus the driving force of the movable core driven by an electromagnetic force is transmitted to the movable contact. This may cause the driving unit to have a complicated structure.